Timeout.swift

import Foundation

private enum TimeoutResult<T> {
    case success(T)
    case timeout
}

struct TimeoutError: Error {}

/// Run an arbitrary async task that is cancelled after a provided timeout interval
func withTimeout<T>(_ timeout: TimeInterval, task: @escaping () async throws -> T) async throws -> T {
    try await withThrowingTaskGroup(of: TimeoutResult<T>.self) { group -> T in
        group.async {
            let value = try await task()
            return .success(value)
        }
        group.async {
            let microseconds = UInt64(timeout * 1_000)
            await Task.sleep(NSEC_PER_MSEC * microseconds)
            return .timeout
        }

        defer { group.cancelAll() }
        switch try await group.next()! {
        case .success(let value):
            return value
        case .timeout:
            throw TimeoutError()
        }
    }
}

Usage.swift

func fetchWithTimeout(from url: URL, timeout: TimeInterval) async throws {
    let (data, response) = try await withTimeout(10.0) {
        try await URLSession.shared.data(from: url, delegate: nil)
    }
    // do stuff
}